The Advent of Code usually attracts quite a few people.
If you want to join in the Racket leaderboard key is: 22197-a7a01707.
raco aoc command for fetching/submitting to Advent of Code: eutro/advent-of-code-racket
Any language in the Racket ecosystem is fine. (Including languages that target other platforms like Urlang and RacketScript.) Edit: some suggestions: Rosette(sudoku example), Racklog, Typed Racket. Or maybe write your own or your own language on Racket, or use Sham to target another platform.
PS thanks to @SamPhillips for creating the Racket leaderboard.